Height adjustable work chairs are used in office environments as well as in industry. These chairs typically include a seat that swivels in relation to the base of the chair. The height adjustment is typically obtained from the construction of the height adjustment mechanism which is usually a gas spring. This gas spring is a telescoping column that includes a gas cylinder that includes a pressurized gas such as nitrogen; a piston extending downwardly from the cylinder which supports the cylinder in an elevated position and includes an end which secures the gas spring to the chair base; and a valve located within the cylinder which allows the movement of gas within the cylinder.
The top of the cylinder is secured within the chair tilt mechanism which is also the mechanism that supports the chair seat and chair back. The chair tilt mechanism is also known as the seat support mechanism. Also included in the tilt mechanism is a lever that actuates the valve located in the gas spring. The valve typically includes a pin extending from the top of the cylinder which when depressed by the lever allows gas to move through the valve and lower the cylinder if a force exceeding gas pressure is applied on the spring or raise the cylinder if no force is applied on the spring.
The gas spring is supported in a vertical position between the chair base and the chair tilt mechanism by a vertical stand tube. The stand tube includes an opening sized so that the cylinder of the gas spring can move vertically yet remain supported by the stand tube regardless of the vertical position of the cylinder.
The gas spring which is responsible for height adjustment in work chairs also allows the seat to swivel in relation to the base. The gas spring cylinder which is secured to the chair seat through the chair tilt mechanism rotates freely in relation to the piston which supports it. It is this rotation which provides the swivel in most work chairs. Additionally the end of the piston which is attached to the chair base may also include ball bearings or other means to allow the piston to rotate in relation to the base while remaining secured to the base. In this way, the gas spring which is a very inexpensive mechanism to manufacture provides both height adjustment and swivel movement of the chair seat in relation to the base.
The swivel movement provided by the gas spring is often in addition to the mobility provided to a work chair through the use of casters. Accordingly, a chair seat may actually be able to rotate or swivel in relation to the floor by the rotation of the gas spring cylinder in relation to the gas spring piston; the rotation of the piston in relation to the chair base; and the rotation of the chair base in relation to the floor through the use of swiveling wheeled casters. The cumulative effect of numerous swivel points tends toward instability of the chair and a lessening of chair control by the user.
Although the swivel movement of the chair seat is generally considered to be desirable for work chairs there are problems associated with this feature. Those who possess a physical or psychological disability and many agile people, as well often experience difficulties in using the chair to stabilize themselves while sitting because of the excessive movement caused by the swiveling seat. This problem is compounded by the inclusion of casters which make the chair even less stable. These same difficulties are also experienced when the chair user attempts to maneuver the chair to different locations.
Should the user of the chair desire to minimize this movement the chair user could replace the chair casters with ones that are pressure braked or lockable. There is, however, no current economical means available to lock a gas spring height adjustable work chair seat against swivel movement. Because of the widespread use of chairs incorporating seat swivel movement, the simple of sitting has become dangerous for many chair users.
Elevated work chairs also benefit from height adjustment but are rendered unstable by seat swivel movement. These work chairs may or may not include swiveling wheel casters. The chairs are elevated for such purposes as to allow a user to be at a proper height to operate machinery controls in an industrial setting or to sit in an elevated position at a drafting table. Mounting or dismounting an elevated swiveling chair has caused numerous injuries in the work place. These injuries are typically caused by the user under correcting, over correcting, or not correcting for the radical swiveling action of the seat. The swiveling action of the seat is a response to the forces inherent with the user's attempted placement of their body onto or off the chair. Climbing onto or off of an elevated swiveling chair has caused numerous injuries in the work environment. These injuries are typically caused by the user missing his or her body placement on the chair due to the radical seat movement associated with excessive swiveling or the chair seat. This causes the user to lose his balance when the chair seat swivels unexpectedly.
An additional problem with excessive chair seat swivel is the inability of the chair user to position the individual spokes of a castered chair base properly under the seat so that the base is able to function as a foot rest. When the user attempts to rotate the chair base through body movement the chair seat swivels which prevents the user from repositioning the chair base as desired.
For the above mentioned reasons there is needed a work chair that inexpensively provides height adjustment through the use of gas springs but also provides a high level of stability by preventing the chair seat from swiveling in relation to the chair base.